a. Field of the Invention
The present invention relates to apparatus and methods for reducing carbon monoxide and unburned hydrocarbons from the exhaust gases of an internal combustion engine.
B. Prior Art
As is known, these toxic pollutants in the exhaust gases must be eliminated as far as possible. They are very abundant when the carburated mixture, drawn in (or sucked) by the engine, is richer in fuel, as when starting a cold engine which is choked. They are also abundant during hot idling of the engine, or during deceleration of the vehicle with very low air intake.
To reduce combustible pollutants (carbon monoxide and hydrocarbons) most prior art processes and apparatus use the injection of air into the exhaust gases, immediately after the exhaust valves, and enable the mixture to remain in a chamber usually called an afterburner reactor, during a period of time sufficient to improve or complete the combustion of unburned components.
The known processes and apparatus exhibit a number of deficiencies, among which include:
Lack of means for quick ignition of the reactor soon after starting up a cold or hot engine.
Excessive internal baffling of the reactor, causing on one hand a delay of the lighting-up, by a heat sink effect, and on the other hand, inducing gases velocities so high that flames are blown--out at high power.
Lack of protection of the flames against the periodic velocities and pressure pulsations of the exhaust gases.
Lack or insufficient amount of bluff-bodies for flame anchoring.
Poor adaptation of the secondary air rate to the variable amount of unburned pollutants, which vary accordingly to the air/fuel ratio (or richness) which is characteristic of the various engine operating conditions.
Such deficiencies are obviously apparent in the DU PONT thermal reactor, as described for instance in Automotive Eng. Feb. 1972 -- p. 27, FIG. 3, which is heavily baffled and completely lacks flame holders. They are also apparent, although to a lesser degree, in the "Rapid Action Manifold" (R.A.M.) described by Robert J. LANG in his paper entitled "A well mixed thermal reactor system for automotive emission control" (SAE 71 0608). This system includes flame-holders located immediately at the outlet of the exhaust valves, which provide a rather quick lighting at start-up of the engine. But the corresponding flames are blownout at high gas throughput and low unburned materials content. As the reactor itself is completely lacking flame-holders and lighting devices, only a very high gas temperature can support combustion, which leads to excessive richness of the fuel mixture sent to the engine intake.